There are known methods of transporting natural gas across bodies of water including for example, through subsea pipelines, by LNG ships as liquefied natural gas or by CNG ships as compressed natural gas (CNG). There are other known means such as converting the gas to gas hydrates or to a diesel-like liquid (GTL) and shipping the hydrates or GTL by ship. Currently, virtually all transport of natural gas across bodies of water is carried out by either subsea pipelines or LNG ships.
The transport of liquefied natural gas (LNG) on ships is a large, well established industry but the transport of compressed natural gas (CNG) by ships or barges is almost non-existent. One of the major impediments to shipping CNG by sea is the cost of a CNG containment system that is suited to ship or barge transport. Thus, there is an ongoing need to design storage systems for compressed gases, such as CNG, that can contain large quantities of CNG and that are particularly suited to installation on or within ships and barges in a way that reduces the overall cost of the CNG ship or barge.
The terrestrial transport of CNG by truck is well known. For decades CNG has been transported in tube-trailers. CNG is a common fuel for motor vehicles and a variety of CNG storage tanks are available for storing fuel in a motor vehicle. Also pipes of various dimensions are often transported by truck or in ships or on barges. It is well known in these industries that by strapping or holding down hexagonally stacked pipe with sufficient force enough friction can be generated to restrict pipes from slipping out of the stack under normal loads. Sometimes a frictional material is placed between the pipe layers to enhance the friction. However, none of these solutions have been able to provide a cost effective CNG ship or barge for the bulk transportation of large quantities of CNG.
One of the preferred methods of constructing a CNG containment system for a ship or barge is to stack pipes longitudinally approximately the full length of the barge or ship in a hexagonal, close spaced fashion. One such method is disclosed in Canadian patent number 2,283,008 filed Sep. 22, 1999. The CNG barge described in this patent had installed on its deck a gas storage assembly, which included a stack of horizontally oriented, long pipes stretching approximately the full length of the barge deck. The stacking was close spaced and one aspect of the invention was that the pipe could be stacked hexagonally together touching one another thus creating a friction bond.
While the barge and ship described in Canadian patent no. 2,283,008 is a possible way to transport CNG, the invention did not take into account the motions of a barge or ship as pitches, yaws, and heaves in response to waves, currents and winds. Nor did it take into account the deflection of the barge or ship itself as it bends, twists and otherwise deflects as it is subjected to the loads caused by the waves. Nor did it take into account the expansion and contraction of the pipes as they are exposed to pressure and temperature changes that will occur as the pipes are loaded and emptied of compressed gas. The flexing and accelerations caused by the sea conditions and the differential temperatures and pressures caused by loading and unloading the pipe will cause the pipes to slide and move relative to each other and relative to the barge or ship.